The Scientist’s Essay for 1. Under Foot

What's important about reasoning and evidence?

to be called “scientific” an explanation must rest on the twin pillars of reasoning and evidence

There are really only two valid ways to support a scientific claim: empirical evidence and logical reasoning from well-established principles. Most often one needs a combination of the two.

In ordinary life, we rarely hold arguments to such high standards. We rely on analogy, anecdote, higher authority, and on hunch and intuition. That's not a criticism. As the great physicist Richard Feynman wrote, “if something is said not to be a science, it does not mean that there's something wrong with it; it just means that it is not a science.” And scientists, too, use those informal ways of thinking as sources of ideas and inspiration. Still, in the end, to be called “scientific” an explanation must rest on the twin pillars of reasoning and evidence.

To offer an explanation in science is to claim that one phenomenon arises as a result of some other phenomenon or process. To say that stars shine because of their luminous character is not an explanation, but just a restatement of the question. To say that stars shine because they are very hot is an explanation, and a surprising one at that. To say that they shine because they are very hot as a result of nuclear reactions occurring at their cores is a more detailed explanation.

An explanation can be scientific and still be wrong. For example, many people will claim that it is hotter in the summer than in the winter because the earth is closer to the sun. In support we might invoke the observations that a source of heat feels more intense when you are closer to it and that in the summer the sunlight feels more intense than in the winter, and perhaps the recalled fact that the earth's orbit isn't perfectly circular. This is a legitimate scientific argument. It just doesn't happen to be correct.

A good scientific explanation accounts for, or is at least consistent with, all the relevant evidence. The idea that summer occurs when the earth is closer to the sun is inconsistent with the fact that when it's summer in New England, it's winter in Argentina. Scientists often come up with tentative explanations (hypotheses) that account for one observation or a few, but then try to consider whether other facts contradict the hypothesis (bad!) or are explained or clarified by it (good!). Attributing the temperature differences among the seasons to the tilt of the earth's axis also accounts for the length of the days, the lack of variation at the equator, and the midnight sun near the poles, among other effects.

This kind of rigorous self-criticism is difficult — we'd all rather think of reasons why we're right than come up with reasons why we're wrong — and even the greatest scientists sometimes fall short. Galileo felt that the existence of the tides provided strong evidence for his contention that the earth rotates, arguing that the rotation causes the oceans to slosh back and forth. But water in a smoothly rotating container doesn't slosh around, and even if it did, why should its sloshing have characteristic daily and monthly periods? (A correct explanation had to wait for Newton's understanding of gravity, and even then it's pretty subtle.)

Fortunately, if not always pleasantly, there are always other scientists around who are only too happy to point out the holes in our arguments. They, too, are playing a crucial role in the development of scientific explanations, and it is important to encourage the skill of respectful scientific disagreement, again based on evidence and reasoning. Criticizing someone else's argument can be difficult and even frightening, especially when it involves contradicting someone you like and/or respect, but it is absolutely essential to the scientific process.

—Roger Tobin